No French King = No French Fleet.

Send out strategic pieces (priests). Map out all French Provinces.

Take your best non-heir General. Take your best units. Max out a stack with your elites... well mixed.

March across Europe or land as close to the French as you can and head hunt the King. If you kill two Kings in a row quickly it tends to wipe out the entire faction far faster then killing off all the princes then the King.

As for protecting your fleets... consolidate them into one or two fleets that are larger then the French. Start mass producing ships asap. Send fleets that outnumber your enemies by at least 2:1 and attack the French fleets smallest groups (get your admirals stars up). Then work your way up to the big guys... in the process the French will have less fleets attacking you as they group to get away from your wolf packs.